Should people who do volunteer work for an organization be thanked by the organization?

Your first inclination may be to say yes. I agree that volunteers should be recognized for their efforts, but why should they be thanked? If you volunteer to work at a hospital, why should some paid member on the staff be thanking you for your work? You certainly did not volunteer to contribute to that person’s salary. You volunteered because you believe in the work being done and because you wanted to support it. Presumably the staff member feels the same way, the only difference being that the staff member decided to make a career of it. I think that it is demeaning to be thanked by that person.